Concentrations of SO_2, NO_x and O_3 and Their Diurnal Variation at Mt. Gokurakuji and Its Vicinity, Hiroshima Prefecture, Western Japan

摘要

Measurements of sulfur dioxide (SO_2), nitrogen oxides (NO_x), ozone (O_3), and meteorological parameters like speeds and wind directions were carried out from February 1997 to February 1998 at 4 sites of Mt. Gokurakuji (the elevation at the summit: 693 m), Hiroshima prefecture, in order to investigate the distribution patterns and diurnal variations of air pollutants with respect to areas of the Japanese red pine forest declines. SO_2 concentrations were low (less than 10 ppb) at every observation site. Higher concentrations of NO_x (80-330 ppb) were observed during the night time and early morning at the sites (altitude 120 m, 130 m) near the city area. NO_x concentration near the summit of Mt. Gokurakuji was as high as 20 ppb at daytime and a few ppb at the nighttime and showed the different patterns of diurnal varitaion from those at the sites near the city area. Concentration of O_3 at the summit was lower during north wind and increased during see breeze, which suggests that photochemically produced O_3 was transported from the city area in which NO_x was emitted. Emission rates of NO_x and the number of vehicles at the surrounding cities of Mt. Gokurakuji have been increased by a factor of 2.5 and 2.0, respectively from 1980 to 1996. Annual concentrations of NO_x at the surrounding cities have been increasing sightly from 1985 and O_x concentrations have also been increasing every year. On the other hand, SO_2 concentrations have been decreasing with the decrease of emission rates of SO_x at the surrounding cities.